This invention relates generally to cooling systems in gas cooled dynamoelectric machines, and particularly to a fan diffuser and collector combination as part of the cooling system.
In dynamoelectric machines, a great amount of heat is generated by the flow of currents through the field and armature windings and by eddy current heating in the stator core laminations. To protect the integrity of the materials of the windings and related supporting elements, a gas is utilized to cool the various components in the machine. In large dynamoelectric machines, the field windings are part of the rotor and the armature windings are part of the stator. The removal of heat from the various components in the dynamoelectric machine requires the gas to be moved through many relatively small passages in the rotor and the stator. Patents issued to Willyoung and Shartrand, U.S. Pat. Nos. 3,348,081 and 3,739,208, respectively, disclose the passages through the rotor and stator laminations as part of a gas cooled dynamoelectric machine. These two patents are incorporated herein by reference thereto.
One method of circulating the gas through the plurality of passages is accomplished by increasing the static pressure or pressure head of the gas at a some point in the cooling system. It is to be understood that there are other methods of circulating the gas through the cooling system of dynamoelectric machines however, this invention is directed towards the method of increasing the static pressure of the gas at a selected point in the cooling system.
Generally, the cooling system of the dynamoelectric machine will include some type of fan mechanism at one or the other or both ends of the machine. The fan is usually located on the rotor at that end. It is to be understood that the detailed description of the invention disclosed herein is directed to one fan, at one end of the dynamoelectric machine, and associated with a cooling system. Since it is common for dynamoelectric machines to include two fans and two interacting cooling systems at both ends of the machine, the invention herein normally would be utilized at both ends of the machine and in both cooling systems. For ease of explanation, the description below relates to only one cooling system which includes one fan at one end of a machine.
The fan circulates the gas through the cooling system by expelling the gas radially through an annular chamber at one end of the dynamoelectric machine. The annular chamber is formed by an inner and an outer end plate shield which are axially spaced apart and located within the frame wrapper. Generally, the frame wrapper surrounds both the stator and the rotor of the machine. The gas passes through an arcuate port in the frame wrapper towards a dome cooler, or means for cooling the gas, which is located atop the frame wrapper. Duct work from the dome cooler to the passages in the frame wrapper allow the gas to pass from the cooler and into the stator laminations as described above.
In a reverse flow cooling system for a dynamoelectric machine, the gas flow is split at the output of the dome cooler. A portion of the cooled gas is directed into the stator, and the remaining portion of the gas is channeled through an annulus duct work into the rotor passages. U.S. Pat. No. 3,739,208, issued to Shartrand, specifically discloses this type of cooling system and that disclosure is incorporated herein by reference thereto. After the gas has been introduced into the stator passages and the rotor passages, and the gas flows through both those elements, the gas eventually enters the air gap between the stator and the rotor and/or the interior space of the frame wrapper. The circulation of the gas is completed by the fan drawing the gas from the region of the stator and the rotor and expelling the gas back into the annular passage at one end of the dynamoelectric machine.
Since the gas must pass through many passages and be directed through and around the various components of the dynamoelectric machine, the primary force which circulates the gas through the machine is the gas' pressure head or its static pressure head. In otherwords, although the velocity of the gas may contribute to some circulation throughout the machine, the gas is moved primarily by its static pressure head. The gas which leaves the fan's exhaust port has an initial static pressure head and an initial velocity pressure head. The annular chamber, which circumferentially surrounds the exhaust port of the fan, does no work on the gas that flows through it. As is well known, Bernoulli's theorum provides that if no work is done on or by an incompressible fluid as it flows, the total head remains unchanged. In otherwords, if the velocity head of the gas changes from one point in the cooling system to another point then the pressure head of the gas must change inversely to the change in the velocity head of the gas. However, it should be recognized that the heating-up or cooling down of the gas is considered as work done on or by the gas, hence eddy streams within the gas flow caused by obstructions to the flow of gas may increase the temperature of the gas and effect the transformation of velocity head into static pressure head.
Although this theorum is relatively well known in the art, the application of this principle to the cooling systems of dynamoelectric machines is not easily accomplished. The annular chamber's axial size, radial dimensions, and its orientation with respect to the fan's exhaust and the other elements of the dynamoelectric machine severely limit the application of Bernoulli's theorum. The orientation of the annular chamber is affected by the end windings which protrude axially towards the fan from the stator of the machine, and the size of the chamber is affected by the frame wrapper which defines the radial extent of the machine, and by the machine's bearings supporting the rotor.
In prior art devices, the annular chamber primarily functioned as a passageway between the exhaust port of the fan and an arcuate port through the frame wrapper which leads to the intake duct for the dome cooler. In some prior art devices, the annular chamber has been a parallel walled passage from the fan exhaust to the arcuate port. Although these prior art devices do transform a portion of the gas' velocity head into static pressure head by virtue of the gas slowing down as it approaches the radial extent of the annular chamber as defined by the frame wrapper, the prior art devices have ignored the eddy streams created in the gas flow by the limited exit from the annular chamber through the arcuate port in the frame wrapper and other obstructions to the flow. These eddy streams cause the gas to heat up, therefore, work is done on the gas by the annular chamber in the form of changing the thermal energy of the gas and the static pressure head of the gas is not enhanced.